1. Field of the Invention
This invention relates to a vertical MOS gate power semiconductor device and a method for manufacturing the same.
2. Background Art
Low breakdown voltage MOSFETs (metal oxide semiconductor field effect transistors) are widely used in AC adapters for notebook personal computers and LCDs (liquid crystal displays) as well as switching power supplies for servers. Conventional examples include a vertical MOSFET having a trench structure in which the current path extends in the thickness direction of the substrate along the sidewall of the trench (see, e.g., Japanese Patent No. 3677489).
An important parameter of such a MOSFET is the product, RON×QSW, of the on-resistance RON, which is the source-drain resistance, and the gate-drain charge QSW (called like “Q-switch”) at the switching time. While RON and QSW are in a tradeoff relationship, it is desired to reduce both of them for speedup.